Recent descriptive mortality analyses, in five U.S. rubber companies, have demonstrated a consistent excess of deaths among rubber workers from malignant neoplasms of the lymphatic and hematopoietic system (LHS). A preliminary case-control study has demonstrated a positive association between lymphatic leukemia and a history of having worked in jobs entailing solvent exposure. A case-control study is proposed drawing on data available from four rubber companies, to seek replication of this leukemia-solvent association and to explore other such associations. Decedent cases dying in the period between 1964 and 1973 with a LHS cancer will each be individually matched with two pairs of controls. All controls will be selected from non-cases with the source populations from which the cases derive and will be matched on sex, race, date of birth and plant. One pair of controls will additionally be matched on year of employment. Complete work-history information will be obtained for all study subjects. This information will be coded according to a comprehensive "Occupational Title" classification system developed by the Occupational Health Studies Group for the rubber industry. Analysis of case-control differences in work history will address three: 1) The association of leukemia (especially lymphatic leukemia) with solvent exposure. 2) The association of other LHS cancer with solvent exposure. 3) The association of any of the LHS cancer with other possibly carcinogenic physico-chemical factors within the work environment. To take account of the full content of employee work histories, elaborate analytic techniques will be used. Estimates of standardized relative risk will be made.